Change of the work function of platinum electrodes induced by halide adsorption

Abstract

SummaryThe properties of a halogen-covered platinum(111) surface have been studied by using density functional theory (DFT), because halides are often present at electrochemical electrode/electrolyte interfaces. We focused in particular on the halogen-induced work function change as a function of the coverage of fluorine, chlorine, bromine and iodine. For electronegative adsorbates, an adsorption-induced increase of the work function is usually expected, yet we find a decrease of the work function for Cl, Br and I, which is most prominent at a coverage of approximately 0.25 ML. This coverage-dependent behavior can be explained by assuming a combination of charge transfer and polarization effects on the adsorbate layer. The results are contrasted to the adsorption of fluorine on calcium, a system in which a decrease in the work function is also observed despite a large charge transfer to the halogen adatom.

First principles study of halogens adsorption on intermetallic surfaces

“…This unusual behavior can be explained as Roman et al [52] suggested, large atoms such as iodine leads to a considerable buildup of charge in the adsorbates-surface bonding regions, and an accompanying electron depletion region far from the surface which creates a net dipole on the adsorbates that in turn promotes a decrease in the work function. The adsorption of chlorine, bromine on Al 2 Au (110) surface increases the work function at low coverages.…”

“…However, as mentioned previously, adsorbates induced surface relaxation of the substrate can also results in a little bit of work function change. The different signs for dipole moment changes and the corresponding work function changes are difficult to interpret with the directly proportional relationship proposed by Roman et al [52] To better illustrate this, we further notice that there is a small intercept in the fitted line. If the calculated dipole moment changes are also very small, this small intercept may cause non-correspondence sign of the work function changes and dipole moment changes.…”

“…The exchange and correlation energy adopts the generalized gradient approximation (GGA) with the PBE functional which developed by Perdew et al [54]. This functional is so widely used because it has been shown to give reliable results in terms of atomization energy [55], chemisorption energies [56], work function changes [52,57], and good estimates of bulk properties of metals [58].…”

“…Fortunately, Leung et al [51] demonstrated the simple relationship between surface dipole moment density and work function change within the framework of local-density formalism for a large number of elements adsorbed on various orientations of W substrates. Roman et al [52] verified that the relationship is also correct for halogens adsorption on Pt (111) surface over a variety of coverages within the framework of generalized gradient approximation. However, to our knowledge, it is still lack of innovative investigation of halogens on intermetallic surfaces to prove the robustness of the linear relationship so far.…”

“…A simple model [51,52] employed in adsorbates on pure metal surfaces illustrates that there is a directly proportional relationship between work function shift and dipole moment change. However, to our knowledge, there is no proof whether it is suited for adsorbates on intermetallic surfaces so far.…”